Zeus, known for his philandering ways, was always on the prowl for beautiful women. The stunning Europa caught his attention and to have an affair with her, he carried her away from Greece and the watchful eyes of Hera. When Zeus abducted Europa, Agenor, who worried for his daughter, sent his sons to find her, with the order not to come back until Europa was returned to him as she was his favorite child. Agenor was quite besotted over his daughter, ready to banish his sons if it meant bringing his daughter back to him.
His five sons left to search for their sister, but most of them were not completely committed to the cause. Phoenix did not go very far from home and settled a land named after him: Phoenicia. Cilix settled in the land that became Cilicia, while Thasus stayed on the island that was named after him. Phineus migrated to Thrace. Thus, all the brothers, except Cadmus, failed to follow through with their father’s command.
Only Cadmus continued his search for his sister. Cadmus went on to Delphi, to seek help from the oracle in finding her. The Pythia (high priestess of Delphi), however, commanded him to abstain from further seeking and to leave Europa to Zeus. The Pythia then told Cadmus that instead he should follow a heifer of a certain kind, and to build a town on the spot where the cow should sink down with fatigue.
Cadmus found the cow described by the oracle among the herds of Pelagon, and followed her into Boeotia, where she sank down on the spot on which Cadmus built Thebes, with the acropolis, Cadmea. As he intended to sacrifice the cow here to Athena, he sent some persons to the neighboring well of Ares to fetch water. This well was guarded by a dragon, a son of Ares, who killed the men sent by Cadmus. Hereupon, Cadmus slew the dragon, and, on the advice of Athena, sowed the teeth of the monster into the earth, out of which armed men grew up, who slew each other, with the exception of five, Echion, Udaeus, Chthonius, Hyperenor, and Pelor. These five, according to the legend, were the ancestors of the Thebans. Although he had followed the orders of the gods, Cadmus was punished for having slain Ares’s dragon by being obliged to serve for a certain period of time (stories range from his sentence being one to five years of service). After his servitude, Athena rewarded him by assigning him the government of Thebes, and Zeus gave him Harmonia for his wife.
Harmonia was the goddess of harmony and concord. As a daughter of Aphrodite, she presided over marital harmony, soothing strife and discord; as a daughter of Ares, she represented harmonious action in war. Late Greek and Roman writers sometimes portrayed her as harmony in the more abstract sense: a deity presiding over the cosmic harmony.
Harmonia was born of Aphrodite's adulterous affair with the god Ares. She was awarded to Cadmus, the hero founder of Thebes, in a wedding attended by all the gods. Hephaestus, however, was still furious over his wife's betrayal, and presented Harmonia with a cursed necklace, which doomed her descendants to endless tragedy. In some versions of the story, Hephaestus gives the necklace to Cadmus to present to his “new wife.” In either case, however, the necklace would be the cause of all the tragedy in the House of Cadmus.
With Harmonia, Cadmus fathered Autonoë, Ino, Semele (the “mother” of Dionysus), Agave, and Polydorus. Though separate lines of the family, Agave & Polydorus would become the great grandparents of Oedipus. Unfortunately, due to the cursed necklace most of this family would meet tragic ends.
Cadmus’ grandson, Actaeon, son of Autonoë and the Thessalian Aristaeüs, was killed when he was still a young man. Actaeon was a great hunter, like his father (Aristaeüs) and his grandmother (Cyrene). One day, Actaeon saw Artemis when the goddess was bathing. It is uncertain whether Actaeon seeing the naked goddess was deliberate or an accident. Either way, Artemis punished Actaeon by turning him into a stag. His own hounds tore the young hunter to pieces.
Cadmus' other daughter, Semele, was seduced by Zeus and became pregnant. The jealous goddess Hera tricked the girl into asking Zeus to appear to her in his real form. Since Zeus had given her any boon the princess could ask of him, he reluctantly agreed. Doing so as god of thunder, he appeared as lightning. Semele died being burnt alive by the lightning. Zeus, however, managed to save their unborn son, Dionysus, by sewing the baby to his thigh. When Dionysus was ready to be born, Zeus opened his thigh to deliver Dionysus. Jealous that their sister had attracted Zeus, Semele's sisters spread lies that her lover was actually mortal, and that her son was illegitimate. They would later be punished by Dionysus.
Ino became the second wife of Athamas, king of Orchomenus. Her jealousy over stepchildren Phrixus and Helle was such that she plotted to have them murdered. However, her plot failed and her stepchildren escaped. She and her husband tried to raise Dionysus by trying to disguise the infant as a girl. Hera, however, saw through the deception. The goddess Hera punished Athamas and Ino by causing them to murder their own sons during a brief spell of madness. Ino tried to kill herself by throwing herself into the sea. She was, however, turned into a minor sea-goddess named Leucothea. As Leucothea, she saved Odysseus, the hero of the Odyssey, after he left the island of Calypso. Ino was often referred to as the White Goddess. In Laconia, she had a sanctuary, where she answered a person's question in a dream. This was her form of the oracle.
The aged Cadmus eventually abdicated his rule in Thebes in favor of his other grandson, Pentheus. Pentheus was son of the Sparti Echion and Agave.
During Pentheus' short reign, Dionysus had become god of wine and ecstasy. When his divine cousin Dionysus came to Thebes and wanted to establish his center of worship in the city, Pentheus had not only refused, he forbade any man or woman to participate in their rite. This was because he believed the rumors that Dionysus' jealous aunts had spread about his mother's pregnancy. To make matters worse, Pentheus also imprisoned many of the Maenads (devoted followers of Dionysus).
In retribution for the family’s actions against him and his mother, Dionysus forced Pentheus' mother Agave and her sisters (Ino and Autonoë) to join the Maenads in their rites. When Pentheus went to the woods to spy on Dionysus' followers, Dionysus caused Pentheus' own mother and aunts to attack the young king. They tore the young king to pieces, thinking Pentheus was a wild beast, a lion or a wild boar. They would by tormented by the guilt of this action for the rest of their lives. This was Dionysus’ ultimate punishment.
After quitting Thebes, Cadmus and Harmonia went to the Cenchelians. These people were at war with the Illyrians, and had received an oracle that promised them victory if they took Cadmus as their commander. The Cenchelians accordingly made Cadmus their king and conquered the enemy. After this, Cadmus had another son, whom he called Illyrius. In the end, Cadmus and Harmonia were changed into dragons, and were removed by Zeus to Elysium.